Piezoelectrical ignition systems



Jan. 11, 1966 J. w. CROWNOVER 3,229,154

PIEZOELECTRICAL IGNITION SYSTEMS Filed June 4, 1962 3 Sheets-Sheet 1Jose :6 M 6rownovez;

I N VE N TQR.

WHA/VN 8 McMA/V/GAL /4 Harvey: for Kl l/kan/ Jan. 11, 1966 J. w.cRowNovE R 3,229,154

PIEZOELECTRICAL IGNITION SYSTEMS Filed June 4, 1962 '5 Sheets-Sheet 2Jose 06 M (ml ma e;

INVENTOR.

WHA/VN 8 McMAN/GAL Afforneys for A a 07km?! 11, 1966 J. w. CROWNOVER 3,

PIEZOELEGTRICAL IGNITION SYSTEMS Filed June 4, 1962 5 Sheets-Sheet 3 Val7 07a F0 rce Jase 0b 1/. Crown 0 ye;

I N VE N TOR.

WHA/VN 8 McMAN/GAL Af/arneys for A Z'Z-am United States Patent 3,229,154lIEZOELECTRICAL IGNITION. SYSTEMS Joseph W. Crownover, La Jolla, Calif.,assignor to McCulloch Corporation, Los Angeles, Calif., 21 corporationof Wisconsin Filed June 4, 1962, Ser. No. 199,949 11 Claims. (Cl.315-55) This invention relates generally to electrical ignition systemsand particularly relates to an electrical system utilizing apiezoelectric element for providing the high voltage impulse required tooperate the spark plug of an internal combustion engine.

Attempts have been made in the past to provide electrical ignitionsystems which make use of a piezoelectric crystal for generating therequired voltage. A piezoelectric crystal will develop an electricalvoltage when it is subjected to mechanical stress. The crystal, whichmay be polycrystalline, has an ordered lattice of ions of oppositecharges. When such a crystal is subjected to mechanical stress the ionsare displaced, and as a result an electrical voltage is developed acrossthe crystal. Various polycrystalline ceramic materials have beendeveloped, which have piezoelectric properties, of which the best knownare barium titanate and lead zirconate-titanate.

In order to develop voltages of the order of 10,000 volts or more whichare required to ignite the combustible mixture in the spark gap of aninternal combustion engine, it has generally been the aim in the past togenerate directly such high voltages. from the piezoelectric ceramic isof the order of 10,000 volts or more, a transformer or spark coil is notneeded which is conventionally used in an ignition system operated froma battery. However, in order to obtain such high voltages from apiezoelectric crystal, it has been found necessary to stress the crystalsuddenly by means of a mechanical impact. Since piezoelectric ceramicsare relatively brittle, care has to be taken when applying the suddenmechanical impact so as not to shatter or break the crystal.Furthermore, many mechanical problems are created when such a suddenmechanical impact is to be provided.

A more important drawback of prior art ignition systems resides in thehigh voltage directly developed by the piezoelectric crystal. In orderto obtain such a high voltage, even with a sudden impact, the crystalhas to be designed in such a way that it has a relatively lowcapacitance. As a result the time constant associated with the crystalwhich depends upon its capacitance and its leakage resistance isrelatively short. This in turn means that the high voltage peaksdeveloped by the piezoelectric crystal will only exist for relativelyshort times, that is, times which are short compared to a cycle of theengine. Hence, a difficult timing problem arises because the highvoltage must be applied to the spark plug with very precise timing orelse the high voltage leaks off before it can be applied to the sparkplug. Furthermore, due to the high voltage developed across thepiezoelectric crystal, it will be obvious that a leakage problem exists.In other words, the high voltage developed across the crystal may easilyleak off due to moisture or other electrical leakage before it can doits Work.

It is accordingly an object of the present invention to provide anignition system including a piezoelectric element which will provide alow output voltage which may then be transformed to a high voltage andwhich is substantially not subject to leakage currents.

Another object of the present invention is to provide an ignition systemfor internal combustion engines which includes a piezoelectric elementhaving a relatively large capacitance and hence a long time constant sothat the precise instant when the voltage pulse developed by the Whenthe voltage obtained "ice piezoelectric element is applied to the sparkgap is not critical.

A further object of the present invention is to provide an electricalignition system of the type referred-to where stress does not have to beapplied as asudden impact to the piezoelectric element to develop therequired output voltage.

Still another object of the invention is to provide an ignition systemwhich includes a piezoelectric crystal utilized as a voltage generatorwhere the peak voltage developed by the piezoelectric crystal is notsubject to leakage.

In accordance with the present invention there is provided an ignitionsystem of the type having a spark gap. The ignition system includes apiezoelectric element as Well as means for mechanically and cyclicallystressing the element to develop a comparatively low votage across thepiezoelectric element. Further means are coupled to the piezoelectricelement for deriving a peak voltage therefrom and transformer means arecoupled in series with the last mentioned means and with the spark gapof the ignition system for delivering a transformed high-voltage pulsewhich is then applied to the spark plug of the system. Preferably, thepiezoelectric element has the form of a cantilever beam to whichmechanical bendingstress is applied cyclically by means synchronizedwith the rotation of the engine shaft. The voltage of one polaritydeveloped across the piezoelectric cantilever beam may either begrounded by means of a switch or may be grounded through a rectifier.The voltage of the opposite polarity is then applied to the transformerand the spark plug through a suitable switch. Alternatively, for atwocylinder engine or an oppositely firing engine, both voltages ofopposite polarity may be utilized.

Instead of utilizing a piezoelectric cantilever beam, it is alsofeasible to provide a stack of piezoelectric discs which are cyclicallycompressed to develop the voltage which is then transformed andthereafter applied to the spark plug.

The novel features that are considered characteristic of this inventionare set forth with particularity in the appended claims. The inventionitself, however, both to its organization and method of operation, aswell as addi tional objects and advantages thereof will be bestunderstood from the following description, when read in con nection withthe accompanying drawings wherein like elements are designated by thesame reference characters, and in which:

FIG. 1 is a side elevational view, partly in section, of a singlecylinder internal combustion engine embodying the ignition system of thepresent invention;

FIG. 2 is a front elevational schematic view of the ignition system ofthe present invention utilizing a cantilever beam construction;

FIG. 3 is a top plan view of the system of FIG. 2;

FIG. 4 is a front elevational schematic view similar to that of FlG. 2of an ignition system in accordance with the present invention andutilizing a rectifier;

FIG. 5 is a chart illustrating the voltages developed across thepiezoelectric element of the system of FIG. 4 as a function of time aswell as the mechanical force applied;

FIG. -6 is a schematic front elevational view and circuit diagram of afurther modification of the invention'utilizing a cantilever beamconstruction; and

FIG. 7 is a schematic elevational view of an ignition system inaccordance with the present invention, utilizing a stack ofpiezoelectric discs.

Referring now to the drawings and particularly FIGS. 1 to 3, there isillustrated, by way. of example, a single cylinder internal combustionengine embodying the ignition system of the present invention. Theengine illustrated in FIG. 1 includes a crankshaft having bearings 11and connected to a piston 12 through a piston rod 13. The piston 12reciprocates in the engine cylinder 14 which may have cooling fins 15. Aspark plug generally indicated at 16 has a pair of electrodes 17 and isdisposed in a combustion chamber 18 of the engine cylinder 14.

Mounted on the crankshaft 10 of the engine is a cam or eccentric 20which rides within retainer 21 to push the lever 22 up and down insynchronism with the movement of the crankshaft 10. As clearly shown inFIGS. 2 and 3, there are provided two cantilever beams 23 whichpreferably have a wide middle portion and tapered ends as illustrated inFIG. 3. The ends of the cantilever beams 23 are mounted on posts 24, forexample, by a screw 25 and a bent-over retainer 26. The lever 22 issecure y mounted to the cantilever beams as indicated at 27 so as topositively move the cantilever beams up and down as indicated by thearrows 28.

Disposed between the cantilever beams 23 there is a piezoelectricelement 30 which preferably is of the same shape as the cantilever beams23. The beams 23 may, for example, be made of steel or any othermaterial which is yieldable or has mechanical compliance. Preferably,the piezoelectric beam 30 consists of a lead zirconate-lead titanateceramic which has the general formula These piezoelectric ceramics arecommonly referred to as lead zirconates. These ceramic materials exhibitan almost linear relationship between the electric charge and themechanical stress up to their elastic limit.

Preferably, the ceramics are heat treated and polarized before use so asto orient the electric charges of the material which is generallypolycrystalline. The electric dipoles formed by the ions of thepiezoelectric material are oriented or poled by an applied electricpotential and then the material is heat treated to obtain a domainorientation which will remain until the material is heated beyond theCurie point. is 300 C., and also its other mechanical and electricalproperties are very favorable for purposes of the invention.

Mounted on the beams 23 is a rod 31 electrically connected to thepiezoelectric beam 30 and which bears one arm 32 of a switch, the otherarm 33 being fixed and grounded as shown. The upper end of the rod 31may be formed to provide another switch contact 34 cooperating with afixed contact 35. Thus, it will be seen that as the lever 22 is moved upand down, the switch 32, 33 and thereafter the switch 34, 35 alternatelyopen and close.

' The switch contact 35 is connected through a lead 36 to the primarywinding 37 of a transformer 38 having a secondary winding 40. The leador conductor 36 may be supported by a fixed and insulated clamp 42. Thelower terminals of the transformer windings 37 and 40 are grounded asshown. The transformer 38 may have an iron core as indicated, or an aircore. The transformer 38 is designed to transform the output voltagederived from the piezoelectric cantilever beam 30 to a higher voltagewhich is then applied 'by a conductor 43 to one of the electrodes 17 ofthe spark plug 16, the other electrode being grounded as shown.

The ignition system of FIGS. 1 to 3 operates as follows: When the engineis running the crankshaft 10 rotates and accordingly the cam 20 rotateswith the crankshaft. As a result the cantilever beams 23 and thepiezoelectric beam 30 are subjected to mechanical bending stress bybeing pushed up and down in synchronism with the rotation of thecrankshaft. Consequently, an electrical voltage is developed across thepiezoelectric beam 30 which varies approximately like a sine wave.During the downward movement of the beams the switch 32, 33 is closedthus grounding the negative voltage, for example, developed across thepiezoelectric beam 30. During the upward motion of the cantilever beamseventually the switch 34, 35

The Curie temperature for lead zircon'atecloses and as a result the peakof the positive voltage is then passed through conductor 36 andimpressed on the primary winding 37. A stepped-up voltage is developedacross the transformers secondary winding 40 which is then impressedacross the spark gap 17, one of the elecrodes of which is grounded. Thisin turn will fire the spark plug and the combustible mixture in theengine cylinder.

Assuming that the force which acts through the lever 22 on thecantilever beams 23 is F and that the stress generated in thepiezoelectric material 30 is F it can then be shown that the force orstress acting on the ceramic is given by the following formula:

F =F 3l+l6t, where l is half the length of the piezoelectric beam 30 andt is the thickness of the beam. By way of example, let it be assumedthat F is 8 pounds, that the beam has a width of one inch, that is, l is1.5 inches and the total thickness t is 0.025 inch. In that case:

Under these conditions the potential generated by the piezoelectricmaterial is 150 volts and the capacitance of the beam is 0.1 microfarad.Furthermore, under these conditions, the pressure per area amounts to3,600 pounds per square inch. It can further be calculated that theresonant frequency of the cantilever beam supported at both endscorresponds to approximately 150 cycles per second. Thus, the beam couldfollow a revolutional speed of the motor up to about ten thousand r.p.m.The above calculations were made with the assumption that the cantileverbeam is rectangular rather than tapered as shown in FIG. '3.

It may also be pointed out that with a capacitance of 0.1 microfarad anda leakage resistance of the order of 10 megohms, the time constant isapproximately one second. This time constant is long compared to themechanical cycle of a single piston combustion engine which may be ofthe order of 300 r.p.m. at the minimum or idle speed corresponding tofive revolutions per second. The operating speed of the engine may be ashigh as r.p. s.

Since the voltage generated by the piezoelectric cantilever beam is ofthe order of volts, the transformer 38 preferably is designed totransform the voltage to approximately 12,000 to 18,000 volts asrequired by the spark plug;

Although a single piston engine has been illustrated in FIG. 1, it willbe understood that the ignition system of the invention is alsoapplicable to multi-cylinder engines. In that case, a conventionaldistributor and timer may be required to distribute the voltagegenerated by the piezoelectric element and applied to the various sparkplugs in cyclic procession.

Referring now to FIG. 4, there is illustrated a modification of theinvention. The ignition system of FIG. 4 utilizes the same cantileverbeam construction as illus trated in FIGS. 1 through 3. However, insteadof providing a switch 32, 33, there is provided a diode or rectifier 50connected by a lead 51 between the rod 31 and ground. Thus, the diodewill act to effectively ground one polarity of the alternating voltagedeveloped across the piezoelectric beam 30 when the beam is stressed.

Furthermore, instead of utilizing a transformer with a primary and asecondary winding, there is illustrated an autotransformer 52 having itslower terminal grounded. The lead 36 is connected to one of the lowerwindings of the autotransformer 52 so as to transform the voltage up.Hence, the peak voltage transferred when the switch 34, 35 closes isapplied to the electrode 117 of the spark plug16. f

The operation of the ignition system of FIG. 4 may best be explained byreference to FIG. 5. In FIG. 5, curve 53 illustrates the mechanicalforce which is applied as a function of time to the piezoelectriccantilever beam 30. This force, as shown by curve 53, varies essentiallylike a sine Wave. In the absence of the rectifier 50 a voltage isdeveloped across the piezoelectric beam 30 which varies essentially likethe curve 54 of FIG. 5. In other words, the voltage varies as a functionof time in a sinusoidal manner.

Curve 55 of FIG. 5 illustrates the eifect of the rectiher 50 on thevoltage developed across the piezoelectric beam 30. The voltageinitially builds up to a miximum value and then begins to fall. As shownby the curve portion 57, when the voltage becomes approximately zero,the rectifier 5t) begins to conduct. Thus, instead of the voltagebecoming negative as shown by the dotted curve portion 56, the voltageremains at approximately zero volts until the voltage begins to riseagain. The voltage now rises, as shown by curve portion 58 during thepositive half cycle. When the peak voltage has been reached, the switch34, 35 closes transferring the voltage to the autotransformer 52.

The curve portion 60 illustrates the effect of the discharge across theelectrode 17 of the spark gap. It will be noticed that there is a highfrequency oscillation which occurs due to the relatively largecapacitance of the system and the low inductance of the auto transformer52. This high frequency oscillation promotes a cleaner discharge throughthe spark gap and a better ignition of the combustible mixture in theengine cylinder.

As pointed out out before, the time constant of the ignition system ofthe invention is relatively large, and hence, the precise instant thevoltage is applied to the spark plug is in no way critical with respectto the piezoelectric element because the voltage does not rapidly leakoff before it can be applied.

Another modification of the present invention is illustated in FIG. 6 towhich reference is now made. Here again there are provided twocantilever beams 23 and a piezoelectric beam 20, which is again operatedthrough the cam 21) and lever 22. However, in FIG. 6, a disc 62 issecured to the crankshaft and bears a switch arm 63 which cooperateswith the fixed switch arm 64. The switch arm 64 is connected through aconductor 65 to the primary winding 37 of the transformer 38. The otherterminal of the primary winding 37 is connected through conductor 66 tothe piezoelectric element 30, thus forming an electric circuit which isclosed through the switch arm 63, 64.

It will thus be seen that every time the crankshaft 10 makes onerevolution, the switch 63, 64 closes to apply a voltage pulse to thetransformer primary winding 37. A stepped-up voltage is obtained fromthe transformer secondary winding 40 which is then applied to one of theelectrodes 17 of the spark plug.

Another switch arm 67 is mounted in a fixed position approximatelyopposite the switch arm as and is grounded as shown. This will serve toground the opposite voltage peak developed when the piezoelectric beam30 is flexed in the opposite direction. Thus, the arrangement of FIG. 6is the equivalent of that shown in FIGS. 1 through 3.

In accordance with the present invention, it is not necessary that thepiezoelectric element be flexed or stressed as explained in connectionwith FIGS. 1 through 6. It is also feasible to compress a pile ofpiezoelectric discs or elements and this has been illustrated in FIG. 7.As shown in FIG. 7, there is provided a plurality of piezoelectric discs7 0 which may, for example, be of a circular form and pressed againstthe fixed support 71 and an end piece 72 of hemispherical shape may beutilized to apply force through a lever 73 pivoted at 74. The lever 73preferably consists of a yieldable material having mechanical compliancesuch as steel. The free end of the lever 73 is in contact with aneccentric or cam 74 which is rotated by a shaft 75 which may, forexample, be the crankshaft of an engine. Between each pair ofpiezoelectric discs 79 there is provided a conductive layer 76 whichmay, for example, be a suitable metallic foil or conductive coatingwhich may consist of silver, copper or brass. As indicated in thedrawings the discs 70 have opposite polarization and are connectedelectrically in parallel. Thus, the conductor 77 is grounded and may beconnected to the negative terminals of the discs 70. The conductor 78connects all the positive terminals of the discs in parallel. Theconductor 78 may be connected to a rotating disc 80 having a switch arm81 cooperating with a fixed switch arm 82 which in turn is connected toone terminal of the primary winding 37 of the transformer 38.

As a result, when the shaft 75 rotates, the discs are cyclicallycompressed to develop during one portion of their cycle, a positivevoltage which is then impressed through the switch 81, 82 upon thetransformer 38 and then to one of the electrodes 17 of the spark plug.

Preferably, an even number of discs is used so that both ends of thestack of discs 74 may be maintained at ground potential.

The capacitance of the discs 70 is approximately the same as that of thebeam previously described. On the other hand, it is possible to obtainan output voltage of 650 volts from the pile of piezoelectric discs ofFIG. '7. This voltage can be obtained with anappliedforce of the orderof 1600 pounds and with a stack of 26 discs having a diameter of 4 inchand a thickness of 0.040 inch. The total capacitance of the discs isapproximately 0.1 microfarad.

There has thus been disclosed an ignition system for internal combustionengines which will develop a voltage suitable for firing the spark plugof the engine. The ignition system includes a piezoelectric elementwhich preferably consists of a lead zirconate ceramic. The piezoelectricelement may either be in the form of a cantilever beam in which case itis cyclically stressed or it may consist of a pile of piezoelectricdiscs which are cyclically compressed. As a result, a relatively lowalternating voltage is developed across the element which may then betransformed to the high voltage required for the spark plug. Thepiezoelectric element has a relatively high capacitance andconsequently, a long time constant which may be of the order of therevolution of the combustion engine or substantially greater.Accordingly, the problem of precisely timing the transfer of the voltageto the spark plug is greatly minimized. Furthermore, leakage of thevoltage is reduced to a minimum. Since the stress applied to thepiezoelectric element can be applied cyclically, there is no need toproduce a sudden impact on the element which may shatter or crack theceramic.

I claim:

1. In an ignition system having a spark gap:

(A) a piezoelectric element having a time constant determined by itscapacitance and its leakage resistance of the order of one second;

(B) means for mechanically and cyclically gradually stressing saidelement to develop a reltaively low varying voltage across said element;

(C) means coupled to said piezoelectric element for deriving a peakvoltage from said piezoelectric element; and

(D) transformer means coupled in series with said means for deriving andthe spark gap for delivering a transformed high voltage pulse.

2. In an ignition system for an internal combustion engine having aspark gap:

(A) an elongated piezoelectric element having a time constant determinedby its capacitance and its leakage resistance which is long compared tothe reciprocal of the mechanical cycle at the idle speed of the internalcombustion engine;

(B) means for mechanically and cyclically bending said element inopposite directions to develop a relatively low alternating voltageacross said element;

(C) means coupled to said piezoelectric element for effectivelygrounding one polarity of said alternating voltage and for deriving apeak voltage of opposite polarity from said piezoelectric element; and

(D) transformer means coupled in series with said means for groundingand the spark gap for deliver-- ing to the spark gap a transformed highvoltage,- pulse.

3. In an ignition system having a spark gap:

(A) an elongated piezoelectric element having a ca-- pacitance of theorder of 0.1 microfarad and a resulting time constant of the order ofone second;

(B) means for mechanically and cyclically bending said element todevelop a relatively low alternating voltage across said element;

(C) switch means coupled to said piezoelectric element for effectivelygrounding one polarity of said alternating voltage and for delivering apeak voltage of: opposite polarity from said piezoelectric element; and

(D) transformer means coupled in series with said switch means and thespark gap for delivering to the spark gap a transformed high voltagepulse.

4. In an ignition system having a spark gap:

(A) an elongated piezoelectric element;

(B) means for mechanically and cyclically bending said element inopposite directions to develop a relatively low alternating voltageacross said element;

(C) a rectifier connected to said piezoelectric element for groundingone polarity of said alternating voltage developed by said piezoelectricelement;

(D) a switch electrically and mechanically connected to saidpiezoelectric element for delivering a peak voltage of oppositepolarity; and

(E) transformer means coupled in series with said switch and the sparkgap for delivering to the spark gap a transformed high voltage pulse.

5. In an ignition system having a spark gap:

(A) a piezoelectric element having a time constant of the order of onesecond determined by its capacitance of the order of 0.1 microfarad andits leakage resistance;

(B) means for mechanically and cyclically gradually compressing anddecompressing said element to develop a relatively low varying voltageacross said element;

(C) means coupled to said piezoelectric element for deriving aunidirectional peak voltage from said piezoelectric element;

(D) and transformer means coupled in series with said means for derivingand the spark gap for delivering to the spark gap a transformed highvoltage pulse.

6. In an ignition system for an internal combustion engine having ashaft and a spark gap:

(A) a piezoelectric cantilever beam;

(B) means operating in synchronism with the rotation of the engine shaftfor mechanically and cyclically applying bending stress to saidpiezoelectric cantilever beam to develop a relatively low cyclicallyvarying voltage thereacross;

(C) a rectifier electrically connected to said piezoelectric beam foreffectively grounding one polarity of said varying voltage;

(D) a transformer for delivering an increased output voltage;

(E) and a switch between said piezoelectric beam and said transformer,said switch being arranged to be closed in timed relation with therotation of the en- 6 applying bending stress to said cantilever beamsand piezoelectric element to develop a relatively-low cyclically-varyingvoltage across said element;

(D) a rectifier electrically connected to said piezoelec tric elementfor effectively grounding one polarity of said varying voltage;

(E) a transformer for delivering an increased output voltage;

(F) and a switch having a terminal connected to said piezoelectricelement and having its other terminal connected to said transformer,said switch being arranged to be closed in timed relation with therotation of the engine shaft to deliver a voltage peak to saidtransformer, and said transformer being coupled across said spark gap,whereby high frequency oscillations are developed across the spark gapupon ignition thereof.

8. In an ignition system for an internal combustion engine having ashaft and a spark gap:

(A) a pair of cantilever beams mounted back to back;

(B) an elongated piezoelectric element disposed be tween said cantileverbeams;

(C) means operating in synchronism with the rotation of the engine shaftfor mechanically and cyclically applying stress to said cantilever beamsand piezoelectric element to develop a relatively-low alternat ingvoltage;

(D) rectifier means electrically connected between said piezoelectricelement and one electrode of the spark p;

(E) a transformer having a primary and a secondary winding fordelivering an increased output voltage;

(F) and a switch having one terminal connected to said piezoelectricelement and having its other terminal connected to said transformer,said switch being arranged to be closed in timed relation with therotation of the engine shaft to deliver a voltage peak to the primarywinding of said transformer, the secondary winding of said transformerbeing connected across said spark gap, whereby high-frequencyoscillations are developed across the spark gap upon ignition thereof.

9. In an ignition system for an internal combustion engine having ashaft and a spark gap:

(A) a piezoelectric cantilever beam;

(B) means operating in synchronism with the rotation of the engine shaftfor mechanically and cyclically applying bending stress to saidpiezoelectric cantilever beam to develop a relatively-low cyclicallyvarying voltage thereacross;

(C) a transformer for delivering an increased output voltage;

(D) and a double-pole, double-throw switch having a first pair ofcontacts electrically connected between said piezoelectric beam and saidtransformer, said switch having a second pair of contacts electricallyconnected between said piezoelectric beam and ground, said switch beingarranged to be closed in timed relation with the rotation of the engineshaft to ground a voltage of one polarity to deliver a voltage peak ofthe opposite polarity to said transformer, and said transformer beingcoupled across said spark p- 10. In an ignition system for an internalcombustion engine having a shaft and a spark gap:

(A) a pair of cantilever beams mounted back to back and having taperedends and a relatively wide central portion;

(B) an elongated piezoelectric element disposed between said cantileverbeams and having a time constant determined by its capacitance andleakage resistance which is long compared to the reciprocal of amechanical cycle at idle speed of the internal combustion engine;

(C) means operating in synchronism with the rotation of the engine shaftfor mechanically and cyclically applying bending stress to the centralportion of said cantilever beams and piezoelectric element to develop arelatively-low alternating voltage across said element;

(D) a transformer for delivering an increased output voltage;

(E) and means including a switch coupled between said piezoelectricelement and transformer and arranged to be closed in timed relation withthe rotation of the engine shaft to deliver a voltage peak to saidtransformer, said transformer being coupled across said spark gap.

11. In an ignition system having a spark gap:

(A) a plurality of piezoelectric elements stacked upon each other withopposite polarity, said elements having a time constant of the order ofone second determined by a capacitance of the order of 0.1 microfaradand the leakage resistance;

(B) means for mechanically and cyclically gradually compressing anddecompressing said elements to develop a relatively-low alternatingvoltage across said elements;

(C) conductor means connected to one end of each of said piezoelectricelements for grounding them and connected to the other end of each ofsaid elements for deriving a peak voltage from said piezoelectricelements;

(D) and transformer means coupled in series with said conductor meansand the spark gap for delivering to the spark gap a transformed highvoltage pulse.

References Cited by the Examiner UNITED STATES PATENTS JOHN W. HUCKERT,Primary Examiner.

20 GEORGE N. WESTBY. DAVID J. GALVIN,

Examiners.

1. IN AN IGNITION SYSTEM HAVING A SPARK GAP: (A) A PIEZOELECTRIC ELEMENTHAVING A TIME CONSTANT DETERMINED BY ITS CAPACITANCE AND ITS LEAKAGERESISTANCE OF THE ORDER OF ONE SECOND; (B) MEANS FOR MECHANICALLY ANDCYCLICALLY GRADUALLY STRESSING SAID ELEMENT TO DEVELOP A RELTAIVELY LOWVARYING VOLTAGE ACROSS SAID ELEMENT; (C) MEANS COUPLED TO SAIDPIEZOELECTRIC ELEMENT FOR DERVING A PEAK VOLTAGE FROM SAID PIEZOELECTRICELEMENT; AND (D) TRANSFORMER MEANS COUPLED IN SERIES WITH SAID MEANS FORDERIVING AND THE SPARK GAP FOR DELIVERING A TRANSFORMED HIGH VOLTAGEPULSE.